1. Field of the Invention
The present invention relates to an inked ribbon cartridge for an impact serial printer, and more particularly to a film ribbon cartridge for use in an impact serial printer or electronic typewriter which is required to have a high quality.
2. Description of the Prior Art
In an impact printer, an inked ribbon such as a cloth ribbon or a carbon film ribbon is used for printing on a paper by impacting it with formed characters or dot-wires. In order to improve the replacement of the inked ribbon, it is contained in a cartridge. Further, in cases where high printing quality is required, a carbon film ribbon is used. However, in view of the nature of the film, it is impossible to form a cartridge having an endless structure which could be repeatedly used for printing as is the case with the inked cloth ribbon.
There has been proposed, as described in the copending U.S. patent application Ser. No. 243,289 assigned to the present assignee, an inked ribbon cartridge having two sets of ribbon feed mechanisms, one for each core means around which the ribbon is wound, allowing the ribbon to travel back and forth so that the cartridge can be loaded upside down when the upper half of the ribbon has been used up thereby doubling the useful life of the cartridge. In this ribbon cartridge, two detent levers always apply a predetermined force to two ratchet wheels which are connected to two core means for preventing an over-rotation of the core means. In this over-rotation preventing mechanism, however, as the ribbon wound on the core is reduced, that is, the diameter of the wound ribbon is reduced, the ribbon tension is significantly increased. This means that more torque is required for taking up the ribbon.